Chemistry at Illinois University of Illinois at Urbana-Champaign

Microanalytical Laboratory

Equipment

All results for elemental analyses are calculated based on a known value of a standard. A computer then calculates the ratio of the sample output to the standard output to arrive at a value.  The standards used are all traceable back to NIST primary standards and all instruments are checked with a NIST primary standards on a regular basis to assure day to day accuracy of results.


All results, unless noted otherwise, will be reported as % by weight.

CHN

CE440 by Exeter Analytical, Inc.


CE440 by Exeter Analytical, Inc.
N. Chelmsford, MA  USA

CHN is an abbreviation for Carbon, Hydron, Nitrogen analyzer.  This instrument detects these and only these three elements. To detect these elements the sample needs to be broken down into its atomic components and then separated. To break the sample down it is combusted in an oxygen atmosphere at 980°C. At this temperature all of the elements to be detected react with oxygen to form CO2, H2O, and NxOy. These gases are carried via a stream of helium gas to a detector. The detector reports a value to the computer which compares it to the known value of a standard. These values are calculated based on the weight of sample. Results are reported in % element by weight.

An aliquot of solid sample is taken and placed in a Sn capsule, weighed, then sealed. An aliquot of liquid sample is aspirated up a capillary glass tube and weighed. The capsule or capillary is then placed in a ladle which is driven into the furnace where combustion takes place.  This is of course a simplified version of what actually goes on.
Listed below are ranges, working detection limits, and instrumental error.
 
 

ELEMENT

RANGE

DETECTION LIMIT

ERROR

C

0-99%

0.10%

0.06%

H

0-85%

0.10%

0.06%

N

0-85%

0.10%

0.06%

Based on a 2.0 mg sample.

 

ICP

OES Optima 2000 DV by Perkin Elmer

OES Optima 2000 DV by Perkin Elmer
Norwalk,CT USA

ICP is an abbreviation for Inductively Coupled Plasma. An ICP is far too complicated to describe here. The basic operating principle is based on intensity of emission from elements  in an excited state.  Digested samples are aspirated into the plasma where a portion of the sample is excited.  (The typical temperature of the plasma is 8,000-10, 000 K.)  The excited elements emit light (UV/VIS) at characteristic wavelengths.  The computer compares the intensity of a sample to the intensity of a known standard.

An inductively coupled plasma is a very high temperature excitation source that desolvates, vaporizes, excited, and ionizes atoms.

The sample is nebulized (sprayed as a very fine vapor) and enters the torch with a flow of argon gas. The argon keeps the torch from melting and is also the plasma itself.

A strong radiofrequency (Rf) generator in the coils around the torch produces an magnetic field which generates the argon plasma.

The temperature in the plasma approaches 10,000 Kelvin in the quartz "torch" shown.

Metal atoms in the plasma are excited to higher energy levels and when they "relax" or return to the ground state, they emit light. The light given off by these atoms is separated into the separate wavelengths by a grating and is detected by a photomulitplier tube.

The atoms give off narrow bands (discrete wavelengths) of emitted light, particular to a given element. In this way, the presence of a particular element can be established. The amount of light given off is also proportional to the amount of that element in the sample, so the concentration of a given element in a sample can be accurately determined.


The above is reprinted, without permission, from Washington State University.

The actual analysis requires only a few minutes. Sample digestion can, however, take up to several days. The ICP is very sensitive and easily detects ppm (part per million) and for some elements ppb (parts per billion). The concentration of the digested sample greatly depends on the amount of sample submitted. If too little sample is submitted the error in the weighing will be large and the concentration of the solution will be low. Both of these will cause large errors in the results. The amount of sample submitted should depend on the element with the lowest concentration.(SEE SAMPLE  SIZE)  A guide to detection limits is listed below.

The ppm detection limits are fixed limits for the instrument The % detection limits listed are based on digestion of 10.00 mg of sample into 100 ml. The % detection limits will be affected as such:

Less sample will RAISE detection limits and
more sample will LOWER detection limits.

DETECTION LIMITS

ELEMENT

%

ppm

ELEMENT

%

ppm

ELEMENT

%

ppm

Ag

0.1

0.1

Hg

0.5

0.5

Rh

0.9

0.9

Al

0.3

0.3

Ho

0.08

0.08

Ru

0.6

0.6

As

0.8

0.8

In

0.8

0.8

S

1.0

1.0

B##

0.1

0.1

Ir

0.4

0.4

Sc

0.03

0.03

Ba

0.1

0.1

K

50

50

Se

0.5

0.5

Be

0.01

0.01

La

0.2

0.2

Si##

0.2

0.2

Bi

0.5

0.5

Li

10

10

Sm

1.0

1.0

Ca

0.01

0.01

Lu

0.1

0.1

Sn##

0.8

0.8

Cd

0.05

0.05

Mg

0.01

0.01

Sr

0.01

0.01

Ce 

0.5

0.5

Mn

0.03

0.03

Ta

0.5

0.5

Co

0.1

0.1

Mo

0.1

0.1

Tb

0.5

0.5

Cr

0.08

0.08

Na

1.0

1.0

Te

0.9

0.9

Cs

**

**

Nb

0.5

0.5

Th

10

10

Cu

0.07

0.07

Ni

1.0

1.0

Te

0.9

0.9

Dy

0.2

0.2

Os

0.1

0.1

Tl

1.0

1.0

Er

0.2

0.2

P

1.0

1.0

U

5.0

5.0

Eu

0.05

0.05

Pb

1.0

1.0

V

0.1

0.1

Fe@@

0.05

0.05

Pd

0.8

0.8

W

0.6

0.6

Ga

0.5

0.5

Pr

0.8

0.8

Y

0.1

0.1

Gd

0.2

0.2

Pt

0.8

0.8

Yb

0.1

0.1

Ge

0.6

0.6

Rb

**

**

Zn

0.05

0.05

Hf

0.2

0.2

Re

0.12

0.12

Zr

0.15

0.15

 
Based on a 10.0 mg sample in 100 ml.

** Cs and Rb cannot be detected by ICP.  AA must be used.  Ask staff for information.  Additional charge
 for Cs, Rb detection.
## Bsi, and Sn are a common and large contaminant in this lab.  The values listed are theoretical instrumental
detection limits.  The amount of contaminant from these elements will only affect extremely low percentages very near the detection limit.
@@  AIR SENSITIVE capsule users should contact the lab staff before requesting Fe.

TGA

TGA7/DSC7 by Perkin Elmer
Norwalk, CT  USA

TGA stands for ThermoGravimetric Analysis. TGA can be used for the determination of decomposition weight loss, combustion analysis, temperature stability, moisture content and reaction mechanism.

TGA monitors weight versus temperature.  It can detect changes in weight of 1 μg. This is accomplished with an extremely sensitive balance hanging inside a furnace.  A thermocouple mounted just a few millimeters from the sample pan ensures accurate temperature of the sample.    There are several events that can be calculated for any run.

Peak, Step, Onset, Delta Y, and First Derivative.

Runs can be measured in (Temp or Time) vs. (Wt% or mg)

 The limits of operation are listed below.

 

Min

Max

Temperature

23 °C

980 °C

Heating Rate

0.1 °C/ min

200 °C/ min

Atmosphere

N2, Air, O2

 

All operating conditions, atmosphere and desired event to calculate must be stated on submission card. (Ex. Ti = 20  Tf = 900  rate = 10°C/min  Hold = 0  calculate = Delta U)  

DSC

DSC stands for Differential Scanning Calorimetery. DSC is used for the determination of endothermic or exothermic reactions or phase changes of a sample. Several characteristics can be determined such as: melting point, curing temperature, reaction kinetics, freezing point, glass transition, physical transitions, heat capacity, reaction mechanism, kinetics, purity, product identification.

DSC monitors heat change  versus temperature input. It can detect changes in heat as low as 1 microwatt. This is accomplished with an extremely sensitive sensor array inside the heater cup. The heater cups have a weight less than 1 gm. This gives them a low thermal mass with extremely quick temperature response and extremely sensitive and accurate heat changes.  (For a more complete description of operation SEE Advanced Guide to Microanalysis.)
 

There are three different atmospheres that can be used on the sample. N2 is nominally used since sample  pans are sealed and therefore not in contact with gas flows. There are several events that can be calculated for any run

Peak, Tg, Onset, Delta Y, Heat Capacity, or first derivative

Runs can be measured in Temp or Time.

NOTE:  Most samples need to be run on a TGA first to determine weight loss at operating temperature in order to protect DSC from unknown samples.

The limits of operation are listed below.

 

Min

Max

Temperature

-40 °C

980 °C

Heating Rate

0.1 °C/ min

200 °C/ min

Cooling Rate

0.1 °C/ min

200 °C/ min

Atmosphere

N2, Air, O2

All operating conditions, atmosphere and desired event to calculate must be stated on submission card. (Ex. Ti = 20  Tf = 900  rate = 10°C/min  Hold = 0  calculate = Delta U)

Microanalysis Laboratory
tel: 217/333-3095
Please call before faxing
fax: 217/333-3095
Rudiger Laufhutte, Lab Manager
laufhutt@uiuc.edu
47 Noyes Laboratory
MC-712 Box 59-1
505 South Mathews Ave.
Urbana, IL 61801

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